Proximal Tibia

For Medical Students

Structure and Location

The proximal tibia flares from a triangular shaft into a broad metaphysis carrying two articular surfaces, the medial and lateral plateaux, separated by the intercondylar area and the tibial spine.

On the front is the tibial tubercle, where the patellar tendon inserts. On the anterolateral surface, at the level of the lateral plateau, is Gerdy's tubercle. On the posterolateral corner is the facet for the fibular head.

Both plateaux are tilted so the back sits lower than the front. That posterior slope is conventionally taught as 7 to 10 degrees and varies between people.

The medial surface is subcutaneous for most of its length, which is why the bone is palpable from the joint line to the ankle and why it is the site chosen for bone graft and for external fixation.

Relations

Anteriorly: the patellar tendon to the tubercle, with the infrapatellar bursa between tendon and bone and the infrapatellar fat pad above.

Medially: the superficial medial collateral ligament inserting below the joint line, and the pes anserinus, the combined insertion of sartorius, gracilis and semitendinosus, lying over it.

Laterally: the iliotibial band to Gerdy's tubercle, and the anterior compartment muscles arising from the lateral surface below that.

Posteriorly: popliteus inserting on the posterior surface above the soleal line, the semimembranosus to the posteromedial corner, and the popliteal vessels crossing before dividing. The anterior tibial artery passes forward through the interosseous membrane at this level.

Function

The proximal tibia receives the load of the whole femoral surface and transmits it into a much narrower shaft. The metaphyseal flare exists to do that.

The two plateaux are not the same shape. The medial is concave and the lateral convex, which is the tibial half of the explanation for the medial side pivoting and the lateral side travelling.

The tubercle is the lever arm of the extensor mechanism, and its position in front of the joint is what allows the quadriceps to extend the knee at all.

Clinical Relevance

Three landmarks locate almost everything: the tubercle in front, Gerdy's tubercle anterolaterally, and the joint line itself, which is found by palpating with the knee flexed.

The subcutaneous medial surface means a fracture here is often open, and that any swelling is immediately apparent.

The anterior tibial artery passing through the interosseous membrane is tethered at that point, in the same way the popliteal artery is tethered above, so the vessel is at risk from displacement at this level.

MRCS Level

Structure and Location

Describe the proximal tibia as a metaphysis with four surfaces and three named prominences.

The articular surfaces: medial plateau concave and larger, lateral plateau convex and smaller, both tilted posteriorly so the plateau slopes down and back.

Between them, the intercondylar area, divided into anterior and posterior parts by the tibial spine, carrying the cruciate and meniscal root attachments. 2.2.3 owns the detail.

The prominences: the tibial tubercle anteriorly, continuous above with a roughened area for the patellar tendon; Gerdy's tubercle anterolaterally for the iliotibial band; and the fibular facet posterolaterally, facing down, back and laterally.

On the posterior surface the soleal line runs obliquely, with popliteus inserting above it and soleus arising below.

Relations

Anterior: patellar tendon, deep and superficial infrapatellar bursae, and the infrapatellar branch of the saphenous nerve crossing obliquely.

Medial layered anatomy, from superficial to deep: the pes anserinus with its bursa, then the superficial medial collateral ligament inserting on the bone below the joint line, then the deep capsular layer attaching to the meniscus and to the bone at the joint margin. The posterior oblique ligament reinforces the posteromedial corner.

Lateral: the iliotibial band to Gerdy's tubercle, with the anterior compartment arising below and behind it, and the biceps femoris and lateral collateral passing to the fibula rather than the tibia.

Posterior: popliteus, the popliteal vessels and tibial nerve, and the origin of soleus below the soleal line. The fibrous arch of soleus tethers the artery here, which is the distal counterpart of the adductor hiatus above.

Posterolateral: the superior tibiofibular joint, a synovial joint with its own capsule, sometimes communicating with the knee.

Blood Supply and Innervation

The metaphysis is supplied by the inferior medial and inferior lateral genicular arteries and by the anterior and posterior tibial recurrent arteries, which ascend to join the genicular anastomosis.

The shaft is supplied by a nutrient artery from the posterior tibial artery entering the posterior surface below the soleal line, and by periosteal vessels. The junction between metaphyseal and diaphyseal supply is the reason the proximal third behaves differently from the middle third in healing.

The anterior tibial artery is the branch of the popliteal that passes forward through the interosseous membrane into the anterior compartment, immediately distal to this region.

Innervation of the periosteum and capsule follows the articular branches of the tibial and common peroneal nerves posteriorly and the recurrent branch of the common peroneal anterolaterally. The infrapatellar branch of the saphenous nerve supplies the skin.

Function

The plateau's posterior slope means the femur sits on an inclined surface, so axial load has a component directed posteriorly. That component is resisted by the cruciates and is why slope is discussed in ligament injury.

The medial plateau being concave and the lateral convex produces asymmetrical constraint: the medial compartment is held, the lateral is free to translate.

The tubercle's position determines the moment arm of the extensor mechanism in the sagittal plane and its alignment relative to the trochlea determines the direction of pull in the axial plane.

Clinical Relevance

Posterior tibial slope is an anatomical feature with a recognised relationship to cruciate loading. The slope is anatomy; whether and how it is measured belongs to 5.16 and to the evidence sections.

The pes anserinus overlying the collateral insertion is the structure harvested for hamstring graft, and the relationship between the two is what makes that harvest possible without destabilising the knee.

Soleus arising below the soleal line gives the posterior approach to the proximal tibia its plane, and the fibrous arch means that approaching proximally and distally to it are different exercises.

The superior tibiofibular joint occasionally communicates with the knee, which explains why a ganglion there can present as a knee problem and why the common peroneal nerve is at risk from a cyst at that site.

FRCS Level

Relations

The proximal tibia is approached anteriorly, anterolaterally, posteromedially and posterolaterally, and the choice is determined by which column of the metaphysis needs exposing rather than by preference.

The structures that define the limits are the patellar tendon anteriorly, the popliteal vessels and the anterior tibial artery's passage posteriorly, and the common peroneal nerve laterally around the fibular neck. The nerve is a relation of the fibula rather than of the tibia, which is why a lateral approach to the tibia is safer than its reputation and a fibular approach is not.

The posteromedial approach uses the interval behind the pes anserinus and in front of the medial head of gastrocnemius, which is the safest route to the posterior plateau.

Function

Plateau geometry sets the constraint of the joint, and surgery on the tibial side changes constraint more directly than surgery on the femoral side, because the tibial surface is the one being shaped.

Slope is the variable with the clearest mechanical consequence: increasing it increases the posteriorly directed component of load and therefore cruciate demand, and reducing it does the reverse.

Tubercle position governs both the sagittal moment arm and the axial direction of extensor pull, so moving it changes two things at once. That is why tubercle procedures are described by the direction of transfer rather than simply as transfers.

Clinical Relevance

Slope modifying osteotomy is a live area, and the anatomy it depends on is on this page. The technique and the indications belong to Section 7.

In plateau fracture work, the column based description of the proximal tibia maps directly onto the approaches above, and the decision about approach precedes the decision about fixation.

The anterior tibial artery's passage through the interosseous membrane is the structure most often forgotten in proximal tibial osteotomy, and it is the reason the level and direction of the cut are constrained.

Bone quality differs across the plateau: the subchondral bone is denser medially where load is habitually higher. That difference affects fixation and subsidence, and it is anatomical rather than pathological.